Such an apparatus for, for example, medical diagnosis or the testing of materials is known from German Offenlegungsschrift 27 46 035. This apparatus is suitable for obtaining layer images of a three-dimensional object within an object zone. The object zones is irradiated from different directions of perspectives with a large number of radiation beams which mutually cover one another. Layer images can then be formed in real time; for example, a frosted glass plate can be moved as desired for the imaging of different object layers. The position of the irradiation plane or the position of the common superposition zone of all radiation beams with respect to the object remains unchanged.
The superposition zone (which is irradiated by all of the radiation beams) has a "rhombic" geometry. The superposition zone tapers from the irradiation plane where the largest dimension of the common superposition zone occurs, as the distance from that irradiation plane increases. Accordingly, the volume which is reconstructed from the perspective images by means of the imaging matrix also has a tapered shape. The image quality of the reconstructed layer images decreases as a function of distance from the irradiation plane, because artefacts are produced in the zone which is not irradiated by all radiation beams and the size of this zone increases with distance from the irradiation plane.
It is an object of the invention to provide a fluoroscopy apparatus which enables the formation of layer images an entire large object, which have consistent quality throughout the object.
This object is achieved in accordance with the invention in that an apparatus of the kind set forth further comprises displacement means for performing a relative movement between the irradiation plane and the object. The displacement means are constructed so that, in any position of the irradiation plane with respect to the object, the imaging elements and the image display device are adjusted for optimum imaging of the irradiation plane.
It is thus achieved that layer images of the same high quality can be obtained of layers which are situated at different locations within an object. To this end, the object is irradiated in a continuous or pulsed manner while the position of the irradiation plane is changed with respect to the object and each time the object layer which is situated within the irradiation plane is reconstructed. The layer images are then directly formed from the coded images. It must be ensured that the irradiation plane is not situated too near to the object surface, because otherwise the radiation load for the object might become excessively high. The position of the irradiation plane in the object can be indicated, for example, by means of a light mark on the object itself. However, it is alternatively possible to indicate in advance a given object zone within which the irradiation plane can be displaced.
The layer images obtained can be processed, for example, electronically and can be displayed on a monitor for the purpose of diagnosis and then electronically stored. After the irradiation, individual layer images can then be fetched for a detailed study. To this end, the image display device is coupled to devices for the display and storage of layer images.
The described fluoroscopy tomosynthesis method is inter alia attractive for use in accident diagnostics, because the physician can very quickly make a diagnosis without time-consuming development of film. The radiation sources are preferably separately activatable, (electrically or mechanically) so that different survey images of the object can also be formed.
Evidently, during fluoroscopy tomosynthesis different layer images can also be formed (in the manner described in German Pat. No. 27 46 035) in each position of the irradiation plane with respect to the object. To this end, for example, the record carrier has a long afterglow time or an image storage effect for the recording of the perspective images, so that it is not continuously necessary to irradiate the object during the formation of the layer images. This operation can be repeated for different positions of the irradiation plane in the object.
In a preferred embodiment in accordance with the invention, the object table is displaceable with respect to the radiation source plane or the radiation sources situated in the radiation source plane are intermittently or continuously displaceable, together with the record carrier, with respect to the object.
As a result, the irradiation plane can be simply displaced as desired with respect to the object, without the position of the irradiation plane with respect to the radiation plane or with respect to the record carrier being changed. This is attractive because coded images at the same scale are obtained wherefrom layer images can be reconstructed at the same scale. To this end, use can be made of an imaging matrix which is arranged at a fixed distance from the record carrier and a layer image display device (for example, a frosted glass plate) which is arranged in a fixed position with respect thereto.